The present invention relates generally to gas turbine engines, and, more specifically, to a seal in an augmenter thereof having a variable exhaust nozzle.
In an augmented turbofan gas turbine engine for powering an aircraft in flight, the augmenter or afterburner is disposed at the aft end of the engine for providing additional thrust when desired. The augmenter includes a liner for containing the hot combustion gases, which liner is surrounded by an annular casing. At the downstream end of the casing is disposed a conventional variable area exhaust nozzle which is adjustable by a plurality of actuators disposed around the circumference of the casing. For example, three actuators may be equiangularly spaced apart, with each actuator having a translatable rod extending from an actuator cylinder, with translation of the rod being suitably converted for pivoting the several flaps of the exhaust nozzle in the various configurations required for operation in the flight envelope.
The engine is suitably mounted within an aircraft engine bay through which is channeled a predetermined amount of air during operation. The afterburner casing has an aft end configured for separating the engine bay from the exhaust nozzle, with the actuators being disposed in the engine bay upstream of the casing aft end. The casing aft end includes respective access openings through which the actuator rods extend for positioning the exhaust nozzle flaps as desired. The bay airflow flows downstream over the actuators and through the access openings and is suitably discharged from the exhaust nozzle.
However, flight testing has shown that under certain operating conditions in the aircraft flight envelope, a reverse differential pressure may be created which can cause flow from the exhaust nozzle through the access openings and upstream into the engine bay. Of course, the air in the exhaust nozzle itself is relatively hot and its leakage into the engine bay may provide a source of combustion ignition for any fuel vapors within the engine bay. The augmenter includes many fuel spraybars each being suitably connected to fuel lines which may leak fuel at some point during the operational lives of the fuel components. In order to reduce the potential for engine bay fires due to ignition from reverse flow of the hot exhaust nozzle air into the engine bay, it is desirable to seal the access openings in the casing aft end through which extend the actuator rods, as well as the access opening provided for a conventional position sensor.